[ModMech]

What the problem could be depends on whichof the three possible controllers you have.

The first two are basically the same, and screw into the left cylinder head at the very rear of the engine. There are MANY things that cause glow-plug problems with these. Best off to update them.

the last type bolts to the rear of the intake, and is fully transistorized. they are VERY reliable, but can suffer from corroded terminals at the controller, bad relays (serviceable part of the controller with squiggly strap bolted to it), and worn out plugs.

Yes, with the last system, if the plugs go out the controller will keep them on for a shorter time the more that do not work. Basically, if three do not work, or have very bad connections, the controller may not come on at all.

There is also the issue of the main connector at the RH side of the engine between the enigne and fender harness. If that 8 or 10 way connector gets corroded, you may not have enough power to the controller for it to function.